diff --git a/man/compton.1.asciidoc b/man/compton.1.asciidoc
index aa0b5fbd..10a87552 100644
--- a/man/compton.1.asciidoc
+++ b/man/compton.1.asciidoc
@@ -199,7 +199,11 @@ OPTIONS
 WIDTH,HEIGHT,ELE1,ELE2,ELE3,ELE4,ELE5...
 ----
 +
-The element in the center must not be included, it will be forever 1.0 or changing based on opacity, depending on whether you have `--blur-background-fixed`. Yet the automatic adjustment of blur factor may not work well with a custom blur kernel.
+In other words, the matrix is formatted as a list of comma separated numbers. The first two numbers must be integers, which specify the width and height of the matrix. They must be odd numbers. Then, the following 'width * height - 1' numbers specifies the numbers in the matrix, row by row, excluding the center element.
++
+The elements are finite floating point numbers. The decimal pointer has to be '.' (a period), and scientific notation is not supported.
++
+The element in the center will either be 1.0 or changing based on opacity, depending on whether you have `--blur-background-fixed`. Yet the automatic adjustment of blur factor may not work well with a custom blur kernel.
 +
 A 7x7 Gaussian blur kernel (sigma = 0.84089642) looks like:
 +
diff --git a/src/config.c b/src/config.c
index 58bf1a30..0c923835 100644
--- a/src/config.c
+++ b/src/config.c
@@ -47,8 +47,8 @@ parse_long(const char *s, long *dest) {
  */
 const char *
 parse_matrix_readnum(const char *src, double *dest) {
-  char *pc = NULL;
-  double val = strtod(src, &pc);
+  const char *pc = NULL;
+  double val = strtod_simple(src, &pc);
   if (!pc || pc == src) {
     log_error("No number found: %s", src);
     return src;
diff --git a/src/string_utils.c b/src/string_utils.c
index df0ac8dd..6b3a8d2a 100644
--- a/src/string_utils.c
+++ b/src/string_utils.c
@@ -40,3 +40,34 @@ void mstrextend(char **psrc1, const char *src2) {
 	strncpy(*psrc1 + len1, src2, len2);
 	(*psrc1)[len - 1] = '\0';
 }
+
+/// Parse a floating point number of form (+|-)?[0-9]*(\.[0-9]*)
+double strtod_simple(const char *src, const char **end) {
+  double neg = 1;
+  if (*src == '-') {
+    neg = -1;
+    src++;
+  } else if (*src == '+') {
+    src++;
+  }
+
+  double ret = 0;
+  while (*src >= '0' && *src <= '9') {
+    ret = ret * 10 + (*src - '0');
+    src++;
+  }
+
+  if (*src == '.') {
+    double frac = 0, mult = 0.1;
+    src++;
+    while (*src >= '0' && *src <= '9') {
+      frac += mult * (*src - '0');
+      mult *= 0.1;
+      src++;
+    }
+    ret += frac;
+  }
+
+  *end = src;
+  return ret * neg;
+}
diff --git a/src/string_utils.h b/src/string_utils.h
index bff0bd6e..8581104a 100644
--- a/src/string_utils.h
+++ b/src/string_utils.h
@@ -11,6 +11,9 @@ char *
 mstrjoin3(const char *src1, const char *src2, const char *src3);
 void mstrextend(char **psrc1, const char *src2);
 
+/// Parse a floating point number of form (+|-)?[0-9]*(\.[0-9]*)
+double strtod_simple(const char *, const char **);
+
 static inline int uitostr(unsigned int n, char *buf) {
   int ret = 0;
   unsigned int tmp = n;